This project is directed at a better understanding of the cellular control mechanisms by which stimuli cause the release of hormones and digestive enzymes and the similar mechanisms which mediate the actions of many hormones. Research is being carried out on the mechanism by which acetylcholine (ACh) and the hormone cholecystokinin (CCK) regulate pancreatic acinar cell function especially enzyme secretion. Studies are being carried out using isolated pancreatic acini prepared from rat and mouse pancreas by digestion with purified collagenase and chymotrypsin. The CCK receptor is studied through binding of iodinated hormone to cellular receptors while ACh will be studied using a labeled competitive antagonist. Mediation of CCK and ACh action by calcium is being studied using radioactive calcium for studies of binding and transport and chlorotetracycline as a fluorescent probe for membrane bound calcium. We are also attempting to introduce the calcium sensitive photoprotein, aequorin, by use of liposomes in order to monitor free intracellular Ca 2 ion. Possible changes in cellular pH or membrane potential as part of the secretory control mechanism will also be studied.